Photoluminescence of the undoped and Bi3+ - Doped Ca3Ga2Ge3O12 garnets

Photoluminescence characteristics of the undoped and Bi3+ - doped Ca3Ga2Ge3O12 garnets are investigated in the 4.2–500 K temperature range by the methods of steady-state and time-resolved spectroscopy. The Bi3+ ions substituting for Ca2+ ions in the garnet Ca3Ga2Ge3O12 and parasitic Ca5Ge3O11 phases are revealed by the X-ray diffraction method. Under excitation in the Bi3+ - related absorption band, the ultraviolet and visible emissions are observed in Ca3Ga2Ge3O12:Bi. The ultraviolet emission bands are ascribed to the radiative decay of the triplet relaxed excited state of Bi3+ ions having different nearest surroundings. A visible emission is found to arise from an exciton localized around a Bi3+ ion. The suggestion is made that the lowest-energy excited level of Bi3+ is located close to the bottom of the conduction band of Ca3Ga2Ge3O12. The mechanisms of the processes, resulting in the appearance of luminescence of the undoped and Bi3+ - doped Ca3Ga2Ge3O12 garnets, are discussed.